Gut microbiome composition may be an indicator of preclinical Alzheimer's disease

The dopaminergic system and Alzheimer's disease

Alzheimer's disease is a common neurodegenerative disorder in older adults. Despite its prevalence, its pathogenesis remains unclear. In addition to the most widely accepted causes, which include excessive amyloid-beta aggregation, tau hyperphosphorylation, and deficiency of the neurotransmitter acetylcholine, numerous studies have shown that the dopaminergic system is also closely associated with the occurrence and development of this condition. Dopamine is a crucial catecholaminergic neurotransmitter in the human body. Dopamine-associated treatments, such as drugs that target dopamine receptor D and dopamine analogs, can improve cognitive function and alleviate psychiatric symptoms as well as ameliorate other clinical manifestations. However, therapeutics targeting the dopaminergic system are associated with various adverse reactions, such as addiction and exacerbation of cognitive impairment. This review summarizes the role of the dopaminergic system in the pathology of Alzheimer's disease, focusing on currently available dopamine-based therapies for this disorder and the common side effects associated with dopamine-related drugs. The aim of this review is to provide insights into the potential connections between the dopaminergic system and Alzheimer's disease, thus helping to clarify the mechanisms underlying the condition and exploring more effective therapeutic options.

The Association Between Constipation and Positron Emission Tomography and Blood-Based Biomarkers in Older Cognitively Unimpaired Adults with Higher Amyloid-β Burden

INTRODUCTION

Constipation may be linked to cognitive decline and a higher risk of Alzheimer's disease (AD). We aimed to investigate the association between constipation and positron emission tomography (PET) and blood-based AD biomarkers in older cognitively unimpaired (CU) adults with higher Aβ burden.

METHODS

Constipation was diagnosed according to Rome IV criteria and the severity of constipation was evaluated by using a validated self-reported questionnaire. The participants underwent the examination of plasma AD biomarkers and 18F-florbetapir PET and 18F-MK6240 PET scans; the latter was only performed in the validation cohort. Correlation and multiple linear regression analyses were used to investigate the association between constipation and AD biomarkers.

RESULTS

Two cohorts were included in our study. A total of 404 older participants with 126 of whom Aβ-PET positive were enrolled in the development cohort. Multiple linear regression analysis showed constipation was associated with plasma t-Tau, p-Tau-181, and neurofilament light chain (NfL) in participants with Aβ-PET (+). Meanwhile, no/mild constipation was associated with lower Aβ-PET standard uptake value ratio. The association between constipation and plasma biomarkers was different in the subgroups stratified by age, sex and APOE ε4 genotype. The above associations were further validated in the validation cohort containing 36 Aβ-PET (+) participants. Importantly, no/mild constipation was associated with less Tau burden evaluated by 18F-MK6240 PET Braak stages.

CONCLUSION

Our data indicate that no/mild constipation may be associated with lower plasma t-Tau, p-Tau-181, and NfL as well as less Aβ and Tau burden in older CU adults with Aβ deposition. Improving constipation and being away from defecation disorders may help reduce the risk of AD development.

Caloric restriction mimetics improve gut microbiota: a promising neurotherapeutics approach for managing age-related neurodegenerative disorders

The gut microbiota (GM) produces various molecules that regulate the physiological functionality of the brain through the gut-brain axis (GBA). Studies suggest that alteration in GBA may lead to the onset and progression of various neurological dysfunctions. Moreover, aging is one of the prominent causes that contribute to the alteration of GBA. With age, GM undergoes a shift in population size and species of microflora leading to changes in their secreted metabolites. These changes also hamper communications among the HPA (hypothalamic-pituitary-adrenal), ENS (enteric nervous system), and ANS (autonomic nervous system). A therapeutic intervention that has recently gained attention in improving health and maintaining communication between the gut and the brain is calorie restriction (CR), which also plays a critical role in autophagy and neurogenesis processes. However, its strict regime and lifelong commitment pose challenges. The need is to produce similar beneficial effects of CR without having its rigorous compliance. This led to an exploration of calorie restriction mimetics (CRMs) which could mimic CR's functions without limiting diet, providing long-term health benefits. CRMs ensure the efficient functioning of the GBA through gut bacteria and their metabolites i.e., short-chain fatty acids, bile acids, and neurotransmitters. This is particularly beneficial for elderly individuals, as the GM deteriorates with age and the body's ability to digest the toxic accumulates declines. In this review, we have explored the beneficial effect of CRMs in extending lifespan by enhancing the beneficial bacteria and their effects on metabolite production, physiological conditions, and neurological dysfunctions including neurodegenerative disorders.

Slow gut transit increases the risk of Alzheimer's disease: An integrated study of the bi-national cohort in South Korea and Japan and Alzheimer's disease model mice

INTRODUCTION

Although the association between Alzheimer's disease (AD) and constipation is controversial, its causality and underlying mechanisms remain unknown.

OBJECTIVES

To investigate the potential association between slow gut transit and AD using epidemiological data and a murine model.

METHODS

We conducted a bi-national cohort study in South Korea (discovery cohort, N=3,130,193) and Japan (validation cohort, N=4,379,285) during the pre-observation period to determine the previous diagnostic history (2009-2010) and the follow-up period (2011-2021). To evaluate the causality, we induced slow gut transit using loperamide in 5xFAD transgenic mice. Changes in amyloid-beta (Aβ) and other markers were examined using ELISA, qRT-PCR, RNA-seq, and behavioral tests.

RESULTS

Constipation was associated with an increased risk of AD in the discovery cohort (hazard ratio, 2.04; 95% confidence interval [CI], 2.01-2.07) and the validation cohort (hazard ratio; 2.82; 95% CI, 2.61-3.05). We found that loperamide induced slower gut transit in 5xFAD mice, increased Aβ and microglia levels in the brain, increased transcription of genes related to norepinephrine secretion and immune responses, and decreased the transcription of defense against bacteria in the colonic tissue.

CONCLUSION

Impaired gut transit may contribute to AD pathogenesis via the gut-brain axis, thus suggesting a cyclical relationship between intestinal barrier disruption and Aβ accumulation in the brain. We propose that gut transit or motility may be a modifiable lifestyle factor in the prevention of AD, and further clinical investigations are warranted.

Neuroprotective effects of mesenchymal stromal cells in mouse models of Alzheimer's Disease: The Mediating role of gut microbes and their metabolites via the Microbiome-Gut-Brain axis

The intricacy and multifaceted nature of Alzheimer's disease (AD) necessitate therapies that target multiple aspects of the disease. Mesenchymal stromal cells (MSCs) emerge as potential agents to mitigate AD symptoms; however, whether their therapeutic efficacy involves modulation of gut microbiota and the microbiome-gut-brain axis (MGBA) remains unexplored. In this study, we evaluated the effects of three distinct MSCs types-derived from the umbilical cord (UCMSC), dental pulp (SHED), and adipose tissue (ADSC)-in an APP/PS1 mouse model of AD. In comparison to saline control, MSCs administration resulted in a significant reduction of behavioral disturbances, amyloid plaques, and phosphorylated tau in the hippocampus and frontal cortex, accompanied by an increase in neuronal count and Nissl body density across AD-afflicted brain regions. Through 16S rRNA gene sequencing, we identified partial restoration of gut microbial balance in AD mice post-MSCs treatment, evidenced by the elevation of neuroprotective Akkermansia and reduction of the AD-associated Sphingomonas. To examine whether gut microbiota involved in MSCs efficacy in treating AD, SHED with better anti-inflammatory and gut microbiota recovery effects among three MSCs, and another AD model 5 × FAD mice with earlier and more pathological proteins in brain than APP/PS1, were selected for further studies. Antibiotic-mediated gut microbial inactivation attenuated MSCs efficacy in 5 × FAD mice, implicating the involvement of gut microbiota in the therapeutic mechanism. Functional analysis of altered gut microbiota and targeted bile acid metabolism profiling revealed a significant enhancement in bile acid variety following MSCs therapy. A chief bile acid constituent, taurocholic acid (TCA), was orally administered to AD mice and similarly abated AD symptoms. Nonetheless, the disruption of intestinal neuronal integrity with enterotoxin abrogated the ameliorative impact of both MSCs and TCA treatments. Collectively, our findings substantiate that MSCs confer therapeutic benefits in AD within a paradigm that primarily involves regulation of gut microbiota and their metabolites through the MGBA.

Characterization of gut microbiota dynamics in an Alzheimer's disease mouse model through clade-specific marker-based analysis of shotgun metagenomic data

Alzheimer's disease (AD) is a complex neurodegenerative disorder significantly impairing cognitive faculties, memory, and physical abilities. To characterize the modulation of the gut microbiota in an in vivo AD model, we performed shotgun metagenomics sequencing on 3xTgAD mice at key time points (i.e., 2, 6, and 12 months) of AD progression. Fecal samples from both 3xTgAD and wild-type mice were collected, DNA extracted, and sequenced. Quantitative taxon abundance assessment using MetaPhlAn 4 ensured precise microbial community representation. The analysis focused on species-level genome bins (SGBs) including both known and unknown SGBs (kSGBs and uSGBs, respectively) and also comprised higher taxonomic categories such as family-level genome bins (FGBs), class-level genome bins (CGBs), and order-level genome bins (OGBs). Our bioinformatic results pinpointed the presence of extensive gut microbial diversity in AD mice and showed that the largest proportion of AD- and aging-associated microbiome changes in 3xTgAD mice concern SGBs that belong to the Bacteroidota and Firmicutes phyla, along with a large set of uncharacterized SGBs. Our findings emphasize the need for further advanced bioinformatic studies for accurate classification and functional analysis of these elusive microbial species in relation to their potential bridging role in the gut-brain axis and AD pathogenesis.

Examining the healthy human microbiome concept

Human microbiomes are essential to health throughout the lifespan and are increasingly recognized and studied for their roles in metabolic, immunological and neurological processes. Although the full complexity of these microbial communities is not fully understood, their clinical and industrial exploitation is well advanced and expanding, needing greater oversight guided by a consensus from the research community. One of the most controversial issues in microbiome research is the definition of a 'healthy' human microbiome. This concept is complicated by the microbial variability over different spatial and temporal scales along with the challenge of applying a unified definition to the spectrum of healthy microbiome configurations. In this Perspective, we examine the progress made and the key gaps that remain to be addressed to fully harness the benefits of the human microbiome. We propose a road map to expand our knowledge of the microbiome-health relationship, incorporating epidemiological approaches informed by the unique ecological characteristics of these communities.

Gut microbiome-derived metabolites in Alzheimer's disease: Regulation of immunity and potential for therapeutics

Alzheimer's disease (AD) is the most common neurodegenerative disorder and cause of dementia. Despite the prevalence of AD, there is a lack of effective disease modifying therapies. Recent evidence indicates that the gut microbiome (GMB) may play a role in AD through its regulation of innate and adaptive immunity. Gut microbes regulate physiology through their production of metabolites and byproducts. Microbial metabolites may be beneficial or detrimental to the pathogenesis and progression of inflammatory diseases. A better understanding of the role GMB-derived metabolites play in AD may lead to the development of therapeutic strategies for AD. In this review, we summarize the function of bioactive GMB-derived metabolites and byproducts and their roles in AD models. We also call for more focus on this area in the gut-brain axis field in order to create effective therapies for AD.

A deep learning framework combining molecular image and protein structural representations identifies candidate drugs for pain

Artificial intelligence (AI) and deep learning technologies hold promise for identifying effective drugs for human diseases, including pain. Here, we present an interpretable deep-learning-based ligand image- and receptor's three-dimensional (3D)-structure-aware framework to predict compound-protein interactions (LISA-CPI). LISA-CPI integrates an unsupervised deep-learning-based molecular image representation (ImageMol) of ligands and an advanced AlphaFold2-based algorithm (Evoformer). We demonstrated that LISA-CPI achieved ∼20% improvement in the average mean absolute error (MAE) compared to state-of-the-art models on experimental CPIs connecting 104,969 ligands and 33 G-protein-coupled receptors (GPCRs). Using LISA-CPI, we prioritized potential repurposable drugs (e.g., methylergometrine) and identified candidate gut-microbiota-derived metabolites (e.g., citicoline) for potential treatment of pain via specifically targeting human GPCRs. In summary, we presented that the integration of molecular image and protein 3D structural representations using a deep learning framework offers a powerful computational drug discovery tool for treating pain and other complex diseases if broadly applied.

Gut microbiota as a potential therapeutic target for children with cerebral palsy and epilepsy

Gut microbiota (GM), the "second genome," exerts influence on human health by impacting brain function through the gut-brain axis. This interaction involves various mechanisms, including immune regulation, metabolites, and neuronal pathways. The application of the next-generation sequencing technology provides a revolutionary tool for the study of GM, which contributes to a deeper comprehension of the GM-host relationship. Children with cerebral palsy (CP), a common neurological disorder in children, are more likely to develop epilepsy, which can exacerbate CP symptoms, particularly those related to cognitive impairment and gastrointestinal tract, such as constipation. The current study identified specific changes in the GM of children with CP accompanied by epilepsy. Furthermore, both diet and oral microbiota have the potential to influence the composition of the GM. Interventions with probiotics and dietary fiber based on GM can improve constipation and cognition, and this approach may be a potential therapeutic strategy.

Causal effect of air pollution on the risk of brain health and potential mediation by gut microbiota

OBJECTIVE

Epidemiologic investigations have examined the correlation between air pollution and neurologic disorders and neuroanatomic structures. Increasing evidence underscores the profound influence of the gut microbiota on brain health. However, the existing evidence is equivocal, and a causal link remains uncertain. This study aimed: to determine if there is a causal connection between four key air pollutants, and 42 neurologic diseases, and 1325 distinct brain structures; and to explore the potential role of the gut microbiota in mediating these associations.

METHODS

Univariable Mendelian randomization (UVMR) and multivariable Mendelian randomization (MVMR) models were deployed to estimate the causal impact of air pollutants (including particulate matter [PM] with aerodynamic diameters <2.5 μm [PM2.5], and <10 μm [PM10]; PM2.5 absorbance; and nitrogen oxides [NOx]) on brain health through various Mendelian randomization methodologies. Lastly, the mediating role of the gut microbiome in the connections between the identified pollutants and neurologic diseases and brain structures was systematically examined.

RESULTS

The potential causal associations of PM2.5, PM2.5 absorbance, PM10, and exposure to NOx, with the risks of intracerebral hemorrhage, hippocampal perivascular spaces, large artery strokes, generalized epilepsy with tonic-clonic seizures, Alzheimer's disease, multiple sclerosis, anorexia nervosa, post-traumatic stress disorder (PTSD), and 420 brain structures, were investigated by UVMR analysis. Following adjustment for air pollutants by MVMR analysis, the genetic correlations between PM10 exposure and PTSD and multiple sclerosis remained significant and robust. Importantly, we observed that phylum Lentisphaerae may mediate the association between PM10 and multiple sclerosis. Additionally, PM2.5 absorbance with a greater risk of reduced thickness in the left anterior transverse temporal gyrus of Heschl and a decreased area in the right sulcus intermedius primus of Jensen, mediated by genus Senegalimassilia and genus Lachnospiraceae UCG010, respectively. Finally, we provided evidence that Clostridium innocuum and genus Ruminococcus2 may partly mediate the causal effect of NOx on altered thickness in the left transverse temporal cortex and area in the right sulcus intermedius primus of Jensen, respectively.

CONCLUSION

This study established a genetic connection between air pollution and brain health, implicating the gut microbiota as a potential mediator in the relationship between air pollution, neurologic disorders, and altered brain structures.

Microbes as medicine

Over the last two decades, advancements in sequencing technologies have significantly deepened our understanding of the human microbiome's complexity, leading to increased concerns about the detrimental effects of antibiotics on these intricate microbial ecosystems. Concurrently, the rise in antimicrobial resistance has intensified the focus on how beneficial microbes can be harnessed to treat diseases and improve health and offer potentially promising alternatives to traditional antibiotic treatments. Here, we provide a comprehensive overview of both established and emerging microbe-centric therapies, from probiotics to advanced microbial ecosystem therapeutics, examine the sophisticated ways in which microbes are used medicinally, and consider their impacts on microbiome homeostasis and health outcomes through a microbial ecology lens. In addition, we explore the concept of rewilding the human microbiome by reintroducing "missing microbes" from nonindustrialized societies and personalizing microbiome modulation to fit individual microbial profiles-highlighting several promising directions for future research. Ultimately, the advancements in sequencing technologies combined with innovative microbial therapies and personalized approaches herald a new era in medicine poised to address antibiotic resistance and improve health outcomes through targeted microbiome management.

Gut Microbiota Alterations in Alzheimer's Disease: Relation with Cognitive Impairment and Mediterranean Lifestyle

Recently, an association between dysbiosis of the gut microbiota (GMB) and the development of several diseases, such as Alzheimer's disease (AD), has been proposed. Dysbiosis involves changes in microbial diversity influenced by environmental factors, like diet or lifestyle. In this study, we investigated the role of GMB parameters in Spanish AD patients, assessing the impact of adherence to the Mediterranean lifestyle (ML), as well as to characterize these parameters in relation to neuropsychological, neuropsychiatric, emotional, and functionality parameters. A case-control study was conducted to investigate the association between the composition of the GMB and cognitive, emotional, neuropsychiatric, and functionality status in Spanish AD patients, along with a shotgun metagenomics approach. Richness and alpha-diversity were significantly lower in the AD group compared to the controls. PERMANOVA and ANOSIM tests of Bray-Curtis dissimilarity, Aitchison distance, and Jaccard similarity did not showed significant differences in beta-diversity between the two groups. Moreover, associations between various phyla of the AD group and orientation performance, food consumption, and activities of daily living were identified. Dysbiosis observed in Spanish AD patients is characterized by reductions in richness and alpha-diversity, alongside alterations in GMB composition, which may be linked to adherence to the ML and cognitive and functionality symptoms.

Multi-omics analysis reveals the key factors involved in the severity of the Alzheimer's disease

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder with a global impact, yet its pathogenesis remains poorly understood. While age, metabolic abnormalities, and accumulation of neurotoxic substances are potential risk factors for AD, their effects are confounded by other factors. To address this challenge, we first utilized multi-omics data from 87 well phenotyped AD patients and generated plasma proteomics and metabolomics data, as well as gut and saliva metagenomics data to investigate the molecular-level alterations accounting the host-microbiome interactions. Second, we analyzed individual omics data and identified the key parameters involved in the severity of the dementia in AD patients. Next, we employed Artificial Intelligence (AI) based models to predict AD severity based on the significantly altered features identified in each omics analysis. Based on our integrative analysis, we found the clinical relevance of plasma proteins, including SKAP1 and NEFL, plasma metabolites including homovanillate and glutamate, and Paraprevotella clara in gut microbiome in predicting the AD severity. Finally, we validated the predictive power of our AI based models by generating additional multi-omics data from the same group of AD patients by following up for 3 months. Hence, we observed that these results may have important implications for the development of potential diagnostic and therapeutic approaches for AD patients.

Investigating the uncertain causal link between gut microbiota and glaucoma: A genetic correlation and Mendelian randomisation study

BACKGROUND

Glaucoma is the most common cause of irreversible blindness, and gut microbiota (GM) is associated with glaucoma. Whether this association represents a causal role remains unknown. This study aims to assess the potential association and causal link between GM and various forms of glaucoma, emphasising the need for cautious interpretation of the strength of these associations.

METHODS

Employing a two-sample bidirectional Mendelian randomisation (MR) framework with false discovery rate correction and various sensitivity analyses, supplemented by genetic correlation analysis via linkage disequilibrium score regression (LDSC) and colocalisation for European summary-level data between MiBioGen consortium and FinnGen Study, we sought to explore the relationship between GM and glaucoma.

RESULTS

While certain microbial taxa showed potential associations with glaucoma subtypes (e.g., Erysipelotrichaceae with primary angle closure glaucoma, Senegalimassilia with exfoliation glaucoma), the overall findings suggest a complex and not definitively causal relationship between GM and glaucoma. Notably, reverse MR analysis did not establish a significant causal effect of glaucoma on GM composition, and no consistent genetic correlations were observed between GM and glaucoma.

CONCLUSIONS

While our study provides some evidence of associations between specific GM taxa and glaucoma, the results underscore the complexity of these relationships and the need for further research to clarify the potential causal links. The findings highlight the importance of interpreting the gut-eye axis with caution and suggest that while GM may play a role in glaucoma, it is unlikely to be a predominant causal factor.

Unveiling the gut microbiota blueprint of schizophrenia: a multilevel omics approach

Background

Schizophrenia is a persistent incurable mental disorder and is characterized by the manifestation of negative emotions and behaviors with anxiety and depression, fear and insecurity, self-harm and social withdrawal. The intricate molecular mechanisms underlying this phenomenon remain largely elusive. Accumulating evidence points towards the gut microbiota exerting an influence on brain function via the gut-brain axis, potentially contributing to the development of schizophrenia. Therefore, the objective of this study is to delineate the gut microbial composition and metabolic profile of fecal samples from individuals with schizophrenia.

Methods

Liquid chromatography-mass spectrometry (LC-MS) and 16S ribosomal RNA (16S rRNA) gene sequencing were employed to analyze fecal metabolites and gut microbiota profiles in a cohort of 29 patients diagnosed with schizophrenia and 30 normal controls. The microbial composition of fecal samples was determined through the 16S rRNA gene sequencing, and microbial α-diversity and β-diversity indices were calculated. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed to analyze the distribution of samples. The metabolites and gut microbiota exhibiting differential expression were identified through the application of biological variance criteria. Co-occurrence analysis of bacteria and metabolites was conducted using the spearman's rank correlation coefficient and visualized in a circular layout with the Cytoscape software.

Results

The findings of the study indicated a lack of substantial evidence supporting significant disparities in α-diversity and β-diversity between individuals with schizophrenia and normal controls. In terms of metabolomics, a discernible pattern in sample distribution between the two groups was observed. Our analysis has revealed 30 bacterial species and 45 fecal metabolites that exhibited notable differences in abundance between individuals diagnosed with schizophrenia and normal controls. These alterations in multilevel omics have led to the development of a co-expression network associated with schizophrenia. The perturbed microbial genes and fecal metabolites consistently demonstrated associations with amino acid and lipid metabolism, which play essential roles in regulating the central nervous system.

Conclusion

Our results offered profound insights into the impact of imbalanced gut microbiota and metabolism on brain function in individuals with schizophrenia.

Cutting-Edge iPSC-Based Approaches in Studying Host-Microbe Interactions in Neuropsychiatric Disorders

Gut microbiota (GM), together with its metabolites (such as SCFA, tryptophan, dopamine, GABA, etc.), plays an important role in the functioning of the central nervous system. Various neurological and psychiatric disorders are associated with changes in the composition of GM and their metabolites, which puts them in the foreground as a potential adjuvant therapy. However, the molecular mechanisms behind this relationship are not clear enough. Therefore, before considering beneficial microbes and/or their metabolites as potential therapeutics for brain disorders, the mechanisms underlying microbiota-host interactions must be identified and characterized in detail. In this review, we summarize the current knowledge of GM alterations observed in prevalent neurological and psychiatric disorders, multiple sclerosis, major depressive disorder, Alzheimer's disease, and autism spectrum disorders, together with experimental evidence of their potential to improve patients' quality of life. We further discuss the main obstacles in the study of GM-host interactions and describe the state-of-the-art solution and trends in this field, namely "culturomics" which enables the culture and identification of novel bacteria that inhabit the human gut, and models of the gut and blood-brain barrier as well as the gut-brain axis based on induced pluripotent stem cells (iPSCs) and iPSC derivatives, thus pursuing a personalized medicine agenda for neuropsychiatric disorders.

Inflammatory Manifestations Associated With Gut Dysbiosis in Alzheimer's Disease

Recent studies strongly suggest that gut microbiome can influence brain functions and contribute to the development of Alzheimer's disease (AD). However, reported changes in the gut microbiomes in AD patients from different countries are not similar, and more research is needed to reveal the relationships between human microbiomes and AD in diverse ethnic populations. There is also an assumption that microbiome-associated peripheral inflammation might drive the development of sporadic AD. This cross-sectional study is aimed at analyzing the gut microbial profile and exploring potential associations with blood cytokines and some clinical parameters among individuals diagnosed with Alzheimer's in Kazakhstan. Consistent with previous studies, we have found that the microbial landscape in AD reveals specific alterations in the gut microbiome. Specifically, the AD patient group showed a decreased Firmicutes/Bacteroidetes ratio. The differential abundance analysis highlighted a dysbiosis in the gut microbiota of AD patients, marked by a reduced presence of Bifidobacterium, particularly B. breve. In our study, AD patients' altered gut microbiota composition notably features an increased presence of Pseudomonadota like Phyllobacterium and inflammatory bacteria such as Synergistetes and the Christensenellaceae family. The metabolic profiling of the AD microbiome reveals a predominant presence of pathways related to sugar, carrier molecules, tetrapyrrole, pyrimidine biosynthesis, and nucleic acid processing. This analysis also highlighted a marked reduction in SCFA, carbohydrate, polysaccharide, polyamine, and myo-inositol degradation pathways. The increases in the proinflammatory cytokines IL-1a, IL-8, IL-17A, IL-12p40, TNF-β, MCP-1, IL-2, and IL-12p70 and the anti-inflammatory cytokines IL-10 and IL-13 were observed in AD patients. Key variables driving the separation of AD and controls include inflammatory markers (IL-1a and IL-8), growth factors (EGF), lipids (LDL), BMI, and gut microbes, like genus Tyzzerella and Turicibacter and species Parabacteroides distasonis and Bacteroides eggerthii. We have also demonstrated that almost all cytokines strongly correlate with serum adiponectin levels and specific microbial taxa in AD patients. Thus, our findings identify potential microbial and inflammatory signatures in an ethnically distinct cohort of AD patients. These could serve as AD biomarkers and microbiota-based therapeutic targets for treating AD.

Identification of proteotoxic and proteoprotective bacteria that non-specifically affect proteins associated with neurodegenerative diseases

There are no cures for neurodegenerative protein conformational diseases (PCDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Emerging evidence suggests the gut microbiota plays a role in their pathogenesis, though the influences of specific bacteria on disease-associated proteins remain elusive. Here, we reveal the effects of 229 human bacterial isolates on the aggregation and toxicity of Aβ1-42, α-synuclein, and polyglutamine tracts in Caenorhabditis elegans expressing these culprit proteins. Our findings demonstrate that bacterial effects on host protein aggregation are consistent across different culprit proteins, suggesting that microbes affect protein stability by modulating host proteostasis rather than selectively targeting disease-associated proteins. Furthermore, we found that feeding C. elegans proteoprotective Prevotella corporis activates the heat shock response, revealing an unexpected discovery of a microbial influence on host proteostasis. Insight into how individual bacteria affect PCD proteins could open new strategies for prevention and treatment by altering the abundance of microbes.

The Role of Microbial Metabolites in the Progression of Neurodegenerative Diseases-Therapeutic Approaches: A Comprehensive Review

The objective of this review is to provide a comprehensive examination of the role of microbial metabolites in the progression of neurodegenerative diseases, as well as to investigate potential therapeutic interventions targeting the microbiota. A comprehensive literature search was conducted across the following databases: PubMed, Scopus, Web of Science, ScienceDirect, and Wiley. Key terms related to the gut microbiota, microbial metabolites, neurodegenerative diseases, and specific metabolic products were used. The review included both preclinical and clinical research articles published between 2000 and 2024. Short-chain fatty acids have been demonstrated to play a crucial role in modulating neuroinflammation, preserving the integrity of the blood-brain barrier, and influencing neuronal plasticity and protection. Furthermore, amino acids and their derivatives have been demonstrated to exert a significant influence on CNS function. These microbial metabolites impact CNS health by regulating intestinal permeability, modulating immune responses, and directly influencing neuroinflammation and oxidative stress, which are integral to neurodegenerative diseases. Therapeutic strategies, including prebiotics, probiotics, dietary modifications, and fecal microbiota transplantation have confirmed the potential to restore microbial balance and enhance the production of neuroprotective metabolites. Furthermore, novel drug developments based on microbial metabolites present promising therapeutic avenues. The gut microbiota and its metabolites represent a promising field of research with the potential to advance our understanding of and develop treatments for neurodegenerative diseases.

Gut microbiota metabolites: potential therapeutic targets for Alzheimer's disease?

Background

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline in cognitive function, which significantly increases pain and social burden. However, few therapeutic interventions are effective in preventing or mitigating the progression of AD. An increasing number of recent studies support the hypothesis that the gut microbiome and its metabolites may be associated with upstream regulators of AD pathology.

Methods

In this review, we comprehensively explore the potential mechanisms and currently available interventions targeting the microbiome for the improvement of AD. Our discussion is structured around modern research advancements in AD, the bidirectional communication between the gut and brain, the multi-target regulatory effects of microbial metabolites on AD, and therapeutic strategies aimed at modulating gut microbiota to manage AD.

Results

The gut microbiota plays a crucial role in the pathogenesis of AD through continuous bidirectional communication via the microbiota-gut-brain axis. Among these, microbial metabolites such as lipids, amino acids, bile acids and neurotransmitters, especially sphingolipids and phospholipids, may serve as central components of the gut-brain axis, regulating AD-related pathogenic mechanisms including β-amyloid metabolism, Tau protein phosphorylation, and neuroinflammation. Additionally, interventions such as probiotic administration, fecal microbiota transplantation, and antibiotic use have also provided evidence supporting the association between gut microbiota and AD. At the same time, we propose an innovative strategy for treating AD: a healthy lifestyle combined with targeted probiotics and other potential therapeutic interventions, aiming to restore intestinal ecology and microbiota balance.

Conclusion

Despite previous efforts, the molecular mechanisms by which gut microbes act on AD have yet to be fully described. However, intestinal microorganisms may become an essential target for connecting the gut-brain axis and improving the symptoms of AD. At the same time, it requires joint exploration by multiple centers and multiple disciplines.

Identifying and Filling the Chemobiological Gaps of Gut Microbial Metabolites

Human gut microbial metabolites are currently undergoing much research due to their involvement in multiple biological processes that are important for health, including immunity, metabolism, nutrition, and the nervous system. Metabolites exert their effect through interaction with host and bacterial proteins, suggesting the use of "metabolite-mimetic" molecules as drugs and nutraceutics. In the present work, we retrieve and analyze the full set of published interactions of these compounds with human and microbiome-relevant proteins and find patterns in their structure, chemical class, target class, and biological origins. In addition, we use virtual screening to expand (more than 4-fold) the interactions, validate them with retrospective analyses, and use bioinformatic tools to prioritize them based on biological relevance. In this way, we fill many of the chemobiological gaps observed in the published data. By providing these interactions, we expect to speed up the full clarification of the chemobiological space of these compounds by suggesting many reliable predictions for fast, focused experimental testing.

Multi-omics analysis of gut-brain axis reveals novel microbial and neurotransmitter signatures in patients with arteriosclerotic cerebral small vessel disease

Arteriosclerotic cerebral small vessel disease (aCSVD) is a major cause of stroke and dementia. Although its underlying pathogenesis remains poorly understood, both inflammaging and gut microbiota dysbiosis have been hypothesized to play significant roles. This study investigated the role of gut microbiota in the pathogenesis of aCSVD through a comparative analysis of the gut microbiome and metabolome between CSVD patients and healthy controls. The results showed that patients with aCSVD exhibited a marked reduction in potentially beneficial bacterial species, such as Faecalibacterium prausnitzli and Roseburia intestinalis, alongside an increase in taxa from Bacteroides and Proteobacteria. Integrated metagenomic and metabolomic analyses revealed that alterations in microbial metabolic pathways, including LPS biosynthesis and phenylalanine-tyrosine metabolism, were associated with the status of aCSVD. Our findings indicated that microbial LPS biosynthesis and phenylalanine-tyrosine metabolism potentially influenced the symptoms and progression of aCSVD via pro-inflammatory effect and modulation of systemic neurotransmitters, respectively. These results imply that gut microbiota characteristics may serve as indicators for early detection of aCSVD and as potential gut-directed therapeutic intervention target.

Gut Microbiome Compositional and Functional Features Associate with Alzheimer's Disease Pathology

BACKGROUND

The gut microbiome is a potentially modifiable factor in Alzheimer's disease (AD); however, understanding of its composition and function regarding AD pathology is limited.

METHODS

Shallow-shotgun metagenomic data was used to analyze fecal microbiome from participants enrolled in the Wisconsin Microbiome in Alzheimer's Risk Study, leveraging clinical data and cerebrospinal fluid (CSF) biomarkers. Differential abundance and ordinary least squares regression analyses were performed to find differentially abundant gut microbiome features and their associations with CSF biomarkers of AD and related pathologies.

RESULTS

Gut microbiome composition and function differed between people with AD and cognitively unimpaired individuals. The compositional difference was replicated in an independent cohort. Differentially abundant gut microbiome features were associated with CSF biomarkers of AD and related pathologies.

DISCUSSION

These findings enhance our understanding of alterations in gut microbial composition and function in AD, and suggest that gut microbes and their pathways are linked to AD pathology.

Polysaccharides extracted from common buckwheat (Fagopyrum esculentum) attenuate cognitive impairment via suppressing RAGE/p38/NF-κB signaling and dysbiosis in AlCl3-treated rats

Patients may find it challenging to accept several FDA-approved drugs for Alzheimer's disease (AD) treatment due to their unaffordable prices and side effects. Despite the known antioxidant, anti-inflammatory, and microbiota-regulating effects of common buckwheat (Fagopyrum esculentum) polysaccharides (FEP), their specific role in preventing AD has not been determined. Here, this study investigated the preventive effects of FEP on AD development in AlCl3-treated rats. The physical properties of FEP were evaluated using X-ray diffraction, FTIR, TGA, DSC, monosaccharide composition, molecular weight, and scanning electron microscopy. The results demonstrated that FEP administration improved memory and learning ability in AlCl3-treated rats. Additionally, AD pathological biomarkers (APP, BACE1, Aβ1-42, and p-TauSer404), inflammatory-associated proteins (IL-1β, IL-6, TNF-α, and Iba1), and MDA and the RAGE/p38/NF-κB pathway were elevated in AlCl3-treated rats. Moreover, these effects were reversed by the upregulation of LRP1, anti-inflammatory cytokines (IL-4 and IL-10), antioxidant enzymes (SOD and catalase), and autophagy proteins (Atg5, Beclin-1, and LC3B). Furthermore, FEP treatment increased the levels of short-chain fatty acids (SCFAs) and the abundance of SCFAs-producing microbes ([Eubacterium]_xylanophilum_group, Lachnospiraceae_NK4A136_group, Lactobacillus). Overall, FEP mitigated oxidative stress, RAGE/p38/NF-κB-mediated neuroinflammation, and AD-associated proteins by upregulating autophagy and SCFA levels, which led to the amelioration of cognitive impairment through microbiota-gut-brain communication in AlCl3-treated rats.

Gut Microbiome Wellness Index 2 enhances health status prediction from gut microbiome taxonomic profiles

Recent advancements in translational gut microbiome research have revealed its crucial role in shaping predictive healthcare applications. Herein, we introduce the Gut Microbiome Wellness Index 2 (GMWI2), an enhanced version of our original GMWI prototype, designed as a standardized disease-agnostic health status indicator based on gut microbiome taxonomic profiles. Our analysis involves pooling existing 8069 stool shotgun metagenomes from 54 published studies across a global demographic landscape (spanning 26 countries and six continents) to identify gut taxonomic signals linked to disease presence or absence. GMWI2 achieves a cross-validation balanced accuracy of 80% in distinguishing healthy (no disease) from non-healthy (diseased) individuals and surpasses 90% accuracy for samples with higher confidence (i.e., outside the "reject option"). This performance exceeds that of the original GMWI model and traditional species-level α-diversity indices, indicating a more robust gut microbiome signature for differentiating between healthy and non-healthy phenotypes across multiple diseases. When assessed through inter-study validation and external validation cohorts, GMWI2 maintains an average accuracy of nearly 75%. Furthermore, by reevaluating previously published datasets, GMWI2 offers new insights into the effects of diet, antibiotic exposure, and fecal microbiota transplantation on gut health. Available as an open-source command-line tool, GMWI2 represents a timely, pivotal resource for evaluating health using an individual's unique gut microbial composition.

Recent advances in Alzheimer's disease: Mechanisms, clinical trials and new drug development strategies

Alzheimer's disease (AD) stands as the predominant form of dementia, presenting significant and escalating global challenges. Its etiology is intricate and diverse, stemming from a combination of factors such as aging, genetics, and environment. Our current understanding of AD pathologies involves various hypotheses, such as the cholinergic, amyloid, tau protein, inflammatory, oxidative stress, metal ion, glutamate excitotoxicity, microbiota-gut-brain axis, and abnormal autophagy. Nonetheless, unraveling the interplay among these pathological aspects and pinpointing the primary initiators of AD require further elucidation and validation. In the past decades, most clinical drugs have been discontinued due to limited effectiveness or adverse effects. Presently, available drugs primarily offer symptomatic relief and often accompanied by undesirable side effects. However, recent approvals of aducanumab (1) and lecanemab (2) by the Food and Drug Administration (FDA) present the potential in disrease-modifying effects. Nevertheless, the long-term efficacy and safety of these drugs need further validation. Consequently, the quest for safer and more effective AD drugs persists as a formidable and pressing task. This review discusses the current understanding of AD pathogenesis, advances in diagnostic biomarkers, the latest updates of clinical trials, and emerging technologies for AD drug development. We highlight recent progress in the discovery of selective inhibitors, dual-target inhibitors, allosteric modulators, covalent inhibitors, proteolysis-targeting chimeras (PROTACs), and protein-protein interaction (PPI) modulators. Our goal is to provide insights into the prospective development and clinical application of novel AD drugs.

The impact of physical exercise on neuroinflammation mechanism in Alzheimer's disease

Introduction

Alzheimer's disease (AD), a major cause of dementia globally, imposes significant societal and personal costs. This review explores the efficacy of physical exercise as a non-pharmacological intervention to mitigate the impacts of AD.

Methods

This review draws on recent studies that investigate the effects of physical exercise on neuroinflammation and neuronal enhancement in individuals with AD.

Results

Consistent physical exercise alters neuroinflammatory pathways, enhances cognitive functions, and bolsters brain health among AD patients. It favorably influences the activation states of microglia and astrocytes, fortifies the integrity of the blood-brain barrier, and attenuates gut inflammation associated with AD. These changes are associated with substantial improvements in cognitive performance and brain health indicators.

Discussion

The findings underscore the potential of integrating physical exercise into comprehensive AD management strategies. Emphasizing the necessity for further research, this review advocates for the refinement of exercise regimens to maximize their enduring benefits in decelerating the progression of AD.

Mapping Knowledge Landscapes and Emerging Trends in AI for Dementia Biomarkers: Bibliometric and Visualization Analysis

BACKGROUND

With the rise of artificial intelligence (AI) in the field of dementia biomarker research, exploring its current developmental trends and research focuses has become increasingly important. This study, using literature data mining, analyzes and assesses the key contributions and development scale of AI in dementia biomarker research.

OBJECTIVE

The aim of this study was to comprehensively evaluate the current state, hot topics, and future trends of AI in dementia biomarker research globally.

METHODS

This study thoroughly analyzed the literature in the application of AI to dementia biomarkers across various dimensions, such as publication volume, authors, institutions, journals, and countries, based on the Web of Science Core Collection. In addition, scales, trends, and potential connections between AI and biomarkers were extracted and deeply analyzed through multiple expert panels.

RESULTS

To date, the field includes 1070 publications across 362 journals, involving 74 countries and 1793 major research institutions, with a total of 6455 researchers. Notably, 69.41% (994/1432) of the researchers ceased their studies before 2019. The most prevalent algorithms used are support vector machines, random forests, and neural networks. Current research frequently focuses on biomarkers such as imaging biomarkers, cerebrospinal fluid biomarkers, genetic biomarkers, and blood biomarkers. Recent advances have highlighted significant discoveries in biomarkers related to imaging, genetics, and blood, with growth in studies on digital and ophthalmic biomarkers.

CONCLUSIONS

The field is currently in a phase of stable development, receiving widespread attention from numerous countries, institutions, and researchers worldwide. Despite this, stable clusters of collaborative research have yet to be established, and there is a pressing need to enhance interdisciplinary collaboration. Algorithm development has shown prominence, especially the application of support vector machines and neural networks in imaging studies. Looking forward, newly discovered biomarkers are expected to undergo further validation, and new types, such as digital biomarkers, will garner increased research interest and attention.

Gut microbiota changes in patients with Alzheimer's disease spectrum based on 16S rRNA sequencing: a systematic review and meta-analysis

Background

The gut microbiota (GM) is hypothesized to play roles in Alzheimer's disease (AD) pathogenesis. In recent years, many GM composition and abundance investigations in AD patients have been conducted; however, despite this work, some results remain controversial. Therefore, we conducted a systematic review and meta-analysis using 16S ribosomal RNA (16S rRNA) sequencing to explore GM alterations between patients with AD spectrum and healthy controls (HCs).

Methods

A systematic and comprehensive literature search of PubMed, Web of Science, Embase, the Cochrane Library, China National Knowledge Infrastructure, China Biology Medicine disc database, WanFang database and Social Sciences Citation Index databases was conducted from inception to January 2023. Inclusion and exclusion criteria were strictly defined, and two researchers independently screened and extracted information from selected studies. Data quality were evaluated according to the "Cochrane system evaluator manual" and pooled data were comprehensively analyzed using Stata 14 software with standardized mean differences (SMDs) and 95% confidence intervals (95% CIs) used to measure effect sizes. Also, geographical heterogeneity effects (related to cohorts) on GM abundance were examined based on subgroup meta-analyses if sufficient studies reported outcomes. Finally, publication bias was assessed using funnel plots.

Results

Out of 1566 articles, 13 studies involving 581 patients with AD spectrum and 445 HCs were deemed eligible and included in our analysis. In summary, a decreased microbiota alpha diversity and a significantly distinct pattern of clustering with regard to beta diversity were observed in AD spectrum patients when compared with HCs. Comparative analyses revealed a decreased Ruminococcus, Faecalibacterium, Lachnospira, Dialister, Lachnoclostridium, and Roseburia abundance in AD spectrum patients while Phascolarctobacterium, Lactobacillus, and Akkermansia muciniphila were more enriched in patients when compared to HCs. Furthermore, regional variations may have been in play for intestinal microbes such as Bacteroides, Bifidobacterium, and Alistipes.

Conclusion

Our meta-analysis identified alterations in GM abundance in patients with AD spectrum, with 12 genera from four major phyla significantly associated with AD. Moreover, we provided evidence for region-specific alterations in Bacteroides, Bifidobacterium, and Alistipes abundance. These findings may have profound implications for the development of innovative GM-based strategies to prevent and treat AD.

Systematic review registration

https://doi.org/10.37766/inplasy2024.6.0067, identifier INPLASY202460067.

Approved drugs and natural products at clinical stages for treating Alzheimer's disease

Alzheimer's disease (AD) remains the foremost cause of dementia and represents a significant unmet healthcare need globally. The complex pathogenesis of AD, characterized by various pathological and physiological events, has historically challenged the development of anti-AD drugs. However, recent breakthroughs in AD drug development, including the approvals of aducanumab, lecanemab, and sodium oligomannate (GV-971), have ended a nearly two-decade hiatus in the introduction of new AD drugs. These developments have addressed long-standing challenges in AD drug development, marking a substantial shift in the therapeutic landscape of AD. Moreover, natural products (NPs) have shown promise in AD drug research, with several currently under clinical investigation. Their distinct properties and mechanisms of action offer new avenues to complement and enhance existing AD treatment approaches. This review article aims to provide an overview of the recent advancements and prospects in AD therapeutics, focusing on both NPs and approved drugs.

The potential role of gut microbiota-derived metabolites as regulators of metabolic syndrome-associated mitochondrial and endolysosomal dysfunction in Alzheimer's disease

Although the role of gut microbiota (GMB)-derived metabolites in mitochondrial and endolysosomal dysfunction in Alzheimer's disease (AD) under metabolic syndrome remains unclear, deciphering these host-metabolite interactions represents a major public health challenge. Dysfunction of mitochondria and endolysosomal networks (ELNs) plays a crucial role in metabolic syndrome and can exacerbate AD progression, highlighting the need to study their reciprocal regulation for a better understanding of how AD is linked to metabolic syndrome. Concurrently, metabolic disorders are associated with alterations in the composition of the GMB. Recent evidence suggests that changes in the composition of the GMB and its metabolites may be involved in AD pathology. This review highlights the mechanisms of metabolic syndrome-mediated AD development, focusing on the interconnected roles of mitochondrial dysfunction, ELN abnormalities, and changes in the GMB and its metabolites. We also discuss the pathophysiological role of GMB-derived metabolites, including amino acids, fatty acids, other metabolites, and extracellular vesicles, in mediating their effects on mitochondrial and ELN dysfunction. Finally, this review proposes therapeutic strategies for AD by directly modulating mitochondrial and ELN functions through targeting GMB metabolites under metabolic syndrome.

Host-microbe interactions: communication in the microbiota-gut-brain axis

Animals harbor a diverse array of symbiotic micro-organisms that coexist in communities across different body sites. These microbes maintain host homeostasis and respond to environmental insults to impact host physiological processes. Trillions of indigenous microbes reside in the gastrointestinal tract and engage with the host central nervous system (microbiota-gut-brain axis) by modulating immune responses, interacting with gut intrinsic and extrinsic nervous system, and regulating neuromodulators and biochemicals. These gut microbiota to brain signaling pathways are constantly informed by each other and are hypothesized to mediate brain health across the lifespan. In this review, we will examine the crosstalk of gut microbiota to brain communications in neurological pathologies, with an emphasis on microbial metabolites and neuromodulators, and provide a discussion of recent advances that help elucidate the microbiota as a therapeutic target for treating brain and behavioral disorders.

The link between gut microbiome and Alzheimer's disease: From the perspective of new revised criteria for diagnosis and staging of Alzheimer's disease

Over the past decades, accumulating evidence suggests that the gut microbiome exerts a key role in Alzheimer's disease (AD). The Alzheimer's Association Workgroup is updating the diagnostic criteria for AD, which changed the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." Previously, most of studies focus on the correlation between the gut microbiome and amyloid beta deposition ("A"), the initial AD pathological feature triggering the "downstream" tauopathy and neurodegeneration. However, limited research investigated the interactions between the gut microbiome and other AD pathogenesis ("TNIVS"). In this review, we summarize current findings of the gut microbial characteristics in the whole spectrum of AD. Then, we describe the association of the gut microbiome with updated biomarker categories of AD pathogenesis. In addition, we outline the gut microbiome-related therapeutic strategies for AD. Finally, we discuss current key issues of the gut microbiome research in the AD field and future research directions. HIGHLIGHTS: The new revised criteria for Alzheimer's disease (AD) proposed by the Alzheimer's Association Workgroup have updated the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." The associations of the gut microbiome with updated biomarker categories of AD pathogenesis are described. Current findings of the gut microbial characteristics in the whole spectrum of AD are summarized. Therapeutic strategies for AD based on the gut microbiome are proposed.

The association between liver fibrosis score and incident dementia: A nationwide retrospective cohort study

BACKGROUND

We assessed the relationship of liver fibrosis score with incident dementia in a large, national sample.

METHODS

For this retrospective cohort study, data of dementia-free individuals aged 40-69 years were derived from electronic records of the largest healthcare provider in Israel. The association between liver fibrosis score (FIB-4), assessed from routine laboratory measurements, and incident dementia was explored through multivariate cox regression models.

RESULTS

Of the total sample (N = 826,578, mean age 55 ± 8 years at baseline), 636,967 (77%) had no fibrosis, 180,114 (21.8%) had inconclusive fibrosis status and 9497 (1.2%) had high risk for advanced fibrosis. Over a median follow-up of 17 years, 41,089 dementia cases were recorded. Inconclusive liver fibrosis and advanced fibrosis were associated with increased dementia risk (HR = 1.09, 95%CI: 1.07-1.11 and HR = 1.18, 95%CI: 1.10-1.27, respectively). This association remained robust through seven sensitivity analyses.

CONCLUSIONS

Liver fibrosis assessed through a serum-based algorithm may serve as a risk factor for dementia in the general population.

HIGHLIGHTS

Liver fibrosis may predict dementia diagnosis in the general population. Inconclusive liver fibrosis was associated with 9% increased dementia risk. Advanced liver fibrosis was associated with 18% increased dementia risk. Findings remained robust in sensitivity analyses and after adjustments.

Commensal-pathogen dynamics structure disease outcomes during Clostridioides difficile colonization

Gastrointestinal colonization by Clostridioides difficile is common in healthcare settings and ranges in clinical presentation from asymptomatic carriage to lethal C. difficile infection (CDI). We used a systems biology approach to investigate why patients colonized with C. difficile have a range of outcomes. Microbiota-humanization of germ-free mice with fecal samples from toxigenic C. difficile carriers revealed a spectrum of virulence among clade 1 lineages and identified commensal Blautia associated with markers of non-pathogenic colonization. Using gnotobiotic mice engrafted with defined human microbiota, we observed strain-specific CDI severity across clade 1 strains. Yet, mice engrafted with a higher diversity community were protected from severe disease across all strains without suppression of C. difficile colonization. These results indicate that when colonization resistance has been breached without overt infection, commensals can attenuate a diversity of virulent strains without inhibiting pathogen colonization, providing insight into determinants of stable C. difficile carriage.

Exploring the Relationship Between Sporadic Creutzfeldt-Jakob Disease and Gut Microbiota Through a Mendelian Randomization Study

Observational studies have shown gut microbiota changes in sporadic Creutzfeldt-Jakob disease patients, but the causal relationship remains unknown. We aimed to determine any causal links between gut microbiota and this prion disease. Using Mendelian randomization analysis, we examined the causal relationship between gut microbiota composition and sporadic Creutzfeldt-Jakob disease. Data on gut microbiota (N = 18,340) and disease cases (5208) were obtained. Various analysis methods were used, including inverse variance weighted, Mendelian randomization-Egger, weighted median, simple mode, and weighted mode. In addition, MR-PRESSO was used to evaluate horizontal pleiotropy and detect outliers. Pleiotropy and heterogeneity were assessed, and reverse analysis was conducted. Negative associations were found between sporadic Creutzfeldt-Jakob disease and family Defluviitaleaceae, family Ruminococcaceae, genus Butyricicoccus, genus Desulfovibrio, and genus Eubacterium nodatum. Genus Lachnospiraceae UCG010 showed a positive correlation. Reverse analysis indicated genetic associations between the disease and decreased levels of family Peptococcaceae, genus Faecalibacterium, and genus Phascolarctobacterium, as well as increased levels of genus Butyrivibrio. No pleiotropy, heterogeneity, outliers, or weak instrument bias were observed. This study revealed bidirectional causal effects between specific gut microbiota components and sporadic Creutzfeldt-Jakob disease. Certain components demonstrated inhibitory effects on disease pathogenesis, while others were positively associated with the disease. Modulating gut microbiota may provide new insights into prion disease therapies. Further research is needed to clarify mechanisms and explore treatments for sporadic Creutzfeldt-Jakob disease.

Role of the gut microbiome in mediating sex-specific differences in the pathophysiology of Alzheimer's disease

Alzheimer's disease (AD) presents distinct pathophysiological features influenced by biological sex, with women disproportionately affected due to sex-specific genetic, hormonal, and epigenetic factors. This review delves into three critical areas of sex differences in AD: First, we explore how genetic predisposition and hormonal changes, particularly those involving sex-specific modifications, influence susceptibility and progression of the disease. Second, we examine the neuroimmune dynamics in AD, emphasizing variations in microglial activity between sexes during crucial developmental stages and the effects of hormonal interventions on disease outcomes. Crucially, this review highlights the significant role of gut microbiome perturbations in shaping AD pathophysiology in a sex-specific manner, suggesting that these alterations can further influence microglial activity and overall disease trajectory. Third, we provide a viewpoint that advocates for personalized therapeutic strategies that integrate the understanding of hormonal fluctuations and microbiome dynamics into treatment plans in order to optimize patient outcomes.

The role of the gut microbiome in the regulation of astrocytes in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is the most common cause of dementia. AD is characterized pathologically by proteinaceous aggregates composed of amyloid beta (Aβ) and tau as well as progressive neurodegeneration. Concurrently with the buildup of protein aggregates, a strong neuroinflammatory response, in the form of reactive astrocytosis and microgliosis, occurs in the AD brain. It has recently been shown that the gut microbiome (GMB), composed of trillions of bacteria in the human intestine, can regulate both reactive astrocytosis and microgliosis in the context of both amyloidosis and tauopathy. Many studies have implicated microglia in these processes. However, growing evidence suggests that interactions between the GMB and astrocytes have a much larger role than previously thought. In this review, we summarize evidence regarding the gut microbiome in the control of reactive astrocytosis in AD.

Correlation between Alzheimer's Disease and Gastrointestinal Tract Disorders

Alzheimer's disease is the most common cause of dementia globally. The pathogenesis is multifactorial and includes deposition of amyloid-β in the central nervous system, presence of intraneuronal neurofibrillary tangles and a decreased amount of synapses. It remains uncertain what causes the progression of the disease. Nowadays, it is suggested that the brain is connected to the gastrointestinal tract, especially the enteric nervous system and gut microbiome. Studies have found a positive association between AD and gastrointestinal diseases such as periodontitis, Helicobacter pylori infection, inflammatory bowel disease and microbiome disorders. H. pylori and its metabolites can enter the CNS via the oropharyngeal olfactory pathway and may predispose to the onset and progression of AD. Periodontitis may cause systemic inflammation of low severity with high levels of pro-inflammatory cytokines and neutrophils. Moreover, lipopolysaccharide from oral bacteria accompanies beta-amyloid in plaques that form in the brain. Increased intestinal permeability in IBS leads to neuronal inflammation from transference. Chronic inflammation may lead to beta-amyloid plaque formation in the intestinal tract that spreads to the brain via the vagus nerve. The microbiome plays an important role in many bodily functions, such as nutrient absorption and vitamin production, but it is also an important factor in the development of many diseases, including Alzheimer's disease. Both the quantity and diversity of the microbiome change significantly in patients with AD and even in people in the preclinical stage of the disease, when symptoms are not yet present. The microbiome influences the functioning of the central nervous system through, among other things, the microbiota-gut-brain axis. Given the involvement of the microbiome in the pathogenesis of AD, antibiotic therapy, probiotics and prebiotics, and faecal transplantation are being considered as possible therapeutic options.

Kai-xin-san improves cognitive impairment in D-gal and Aβ25-35 induced ad rats by regulating gut microbiota and reducing neuronal damage

ETHNOPHARMACOLOGICAL RELEVANCE

Kai-Xin-San (KXS) is a classic herbal formula for the treatment and prevention of AD (Alzheimer's disease) with definite curative effect, but its mechanism, which involves multiple components, pathways, and targets, is not yet fully understood.

AIM OF THE STUDY

To verify the effect of KXS on gut microbiota and explore its anti-AD mechanism related with gut microbiota.

MATERIALS AND METHODS

AD rat model was established and evaluated by intraperitoneal injection of D-gal and bilateral hippocampal CA1 injections of Aβ25-35. The pharmacodynamics of KXS in vivo includes general behavior, Morris water maze test, ELISA, Nissl & HE staining and immunofluorescence. Systematic analysis of gut microbiota was conducted using 16S rRNA gene sequencing technology. The potential role of gut microbiota in the anti-AD effect of KXS was validated with fecal microbiota transplantation (FMT) experiments.

RESULTS

KXS could significantly improve cognitive impairment, reduce neuronal damage and attenuate neuroinflammation and colonic inflammation in vivo in AD model rats. Nine differential intestinal bacteria associated with AD were screened, in which four bacteria (Lactobacillus murinus, Ligilactobacillus, Alloprevotella, Prevotellaceae_NK3B31_group) were very significant.

CONCLUSION

KXS can maintain the ecological balance of intestinal microbiota and exert its anti-AD effect by regulating the composition and proportion of gut microbiota in AD rats through the microbiota-gut-brain axis.

Perturbations in gut microbiota composition in schizophrenia

Schizophrenia is a severe, complex and long-term psychiatric disorder with unclear etiology. Gut microbes influence the central nervous system via the gut-brain axis. Consequently, investigations of the relationship between gut microbes and schizophrenia are warranted. This study involved 29 patients with schizophrenia and 30 age-matched normal controls. After 16S rRNA gene sequencing and whole-genome shotgun metagenomic sequencing, we analyzed microbial diversity, composition, and function. According to 16S rRNA and metagenomic gene sequencing results, patients with schizophrenia had higher abundances of Clostridium and Megasphaera. Functional analysis showed that sphingolipid, phosphonates and phosphinates, as well as glutamine metabolism were associated with the occurrence and development of schizophrenia. Our data suggest that the gut microbiota exerts an effect on patients with schizophrenia, providing valuable insights into the potential regulation of in the context of this disorder.

An emerging role for the gut microbiome in tauopathy

Tauopathies constitute a group of neurodegenerative diseases characterized by abnormal aggregation of the protein tau, progressive neuronal and synaptic loss, and eventual cognitive and motor impairment. In this review, we will highlight the latest efforts investigating the intricate interplay between the gut microbiome and tauopathies. We discuss the physiological interactions between the microbiome and the brain as well as clinical and experimental evidence that suggests that the presence of tauopathy alters the composition of gut microbiota. We explore both animal and human studies that define causative relationships between the gut microbiome and tauopathy by directly manipulating or transferring gut microbiota. This review highlights future directions into identifying and mechanistically elucidating microbial species causally linked to tauopathies, with an ultimate goal of devising therapeutic targets towards the gut microbiome to treat tauopathies.

Harnessing human microbiomes for disease prediction

The human microbiome has been increasingly recognized as having potential use for disease prediction. Predicting the risk, progression, and severity of diseases holds promise to transform clinical practice, empower patient decisions, and reduce the burden of various common diseases, as has been demonstrated for cardiovascular disease or breast cancer. Combining multiple modifiable and non-modifiable risk factors, including high-dimensional genomic data, has been traditionally favored, but few studies have incorporated the human microbiome into models for predicting the prospective risk of disease. Here, we review research into the use of the human microbiome for disease prediction with a particular focus on prospective studies as well as the modulation and engineering of the microbiome as a therapeutic strategy.

Novel insights into the activating transcription factor 4 in Alzheimer's disease and associated aging-related diseases: Mechanisms and therapeutic implications

Ageing is inherent to all human beings, most mechanistic explanations of ageing results from the combined effects of various physiological and pathological processes. Additionally, aging pivotally contributes to several chronic diseases. Activating transcription factor 4 (ATF4), a member of the ATF/cAMP response element-binding protein family, has recently emerged as a pivotal player owing to its indispensable role in the pathophysiological processes of Alzheimer's disease and aging-related diseases. Moreover, ATF4 is integral to numerous biological processes. Therefore, this article aims to comprehensively review relevant research on the role of ATF4 in the onset and progression of aging-related diseases, elucidating its potential mechanisms and therapeutic approaches. Our objective is to furnish scientific evidence for the early identification of risk factors in aging-related diseases and pave the way for new research directions for their treatment. By elucidating the signaling pathway network of ATF4 in aging-related diseases, we aspire to gain a profound understanding of the molecular and cellular mechanisms, offering novel strategies for addressing aging and developing related therapeutics.

Sex-specific associations between AD genotype and the microbiome of human amyloid beta knock-in (hAβ-KI) mice

INTRODUCTION

Emerging evidence links changes in the gut microbiome to late-onset Alzheimer's disease (LOAD), necessitating examination of AD mouse models with consideration of the microbiome.

METHODS

We used shotgun metagenomics and untargeted metabolomics to study the human amyloid beta knock-in (hAβ-KI) murine model for LOAD compared to both wild-type (WT) mice and a model for early-onset AD (3xTg-AD).

RESULTS

Eighteen-month female (but not male) hAβ-KI microbiomes were distinct from WT microbiomes, with AD genotype accounting for 18% of the variance by permutational multivariate analysis of variance (PERMANOVA). Metabolomic diversity differences were observed in females, however no individual metabolites were differentially abundant. hAβ-KI mice microbiomes were distinguishable from 3xTg-AD animals (81% accuracy by random forest modeling), with separation primarily driven by Romboutsia ilealis and Turicibacter species. Microbiomes were highly cage specific, with cage assignment accounting for more than 40% of the PERMANOVA variance between the groups.

DISCUSSION

These findings highlight a sex-dependent variation in the microbiomes of hAβ-KI mice and underscore the importance of considering the microbiome when designing studies that use murine models for AD.

HIGHLIGHTS

Microbial diversity and the abundance of several species differed in human amyloid beta knock-in (hAβ-KI) females but not males. Correlations to Alzheimer's disease (AD) genotype were stronger for the microbiome than the metabolome. Microbiomes from hAβ-KI mice were distinct from 3xTg-AD mice. Cage effects accounted for most of the variance in the microbiome and metabolome.

Multi-omics Analysis Reveals Key Gut Microbiota and Metabolites Closely Associated with Huntington's Disease

Dysbiosis of the gut microbiota is closely associated with neurodegenerative diseases, including Huntington's disease (HD). Gut microbiome-derived metabolites are key factors in host-microbiome interactions. This study aimed to investigate the crucial gut microbiome and metabolites in HD and their correlations. Fecal and serum samples from 11 to 26 patients with HD, respectively, and 16 and 23 healthy controls, respectively, were collected. The fecal samples were used for shotgun metagenomics while the serum samples for metabolomics analysis. Integrated analysis of the metagenomics and metabolomics data was also conducted. Firmicutes, Bacteroidota, Proteobacteria, Uroviricota, Actinobacteria, and Verrucomicrobia were the dominant phyla. At the genus level, the presence of Bacteroides, Faecalibacterium, Parabacteroides, Alistipes, Dialister, and Christensenella was higher in HD patients, while the abundance of Lachnospira, Roseburia, Clostridium, Ruminococcus, Blautia, Butyricicoccus, Agathobaculum, Phocaeicola, Coprococcus, and Fusicatenibacter decreased. A total of 244 differential metabolites were identified and found to be enriched in the glycerophospholipid, nucleotide, biotin, galactose, and alpha-linolenic acid metabolic pathways. The AUC value from the integrated analysis (1) was higher than that from the analysis of the gut microbiota (0.8632). No significant differences were found in the ACE, Simpson, Shannon, Sobs, and Chao indexes between HD patients and controls. Our study determined crucial functional gut microbiota and potential biomarkers associated with HD pathogenesis, providing new insights into the role of the gut microbiota-brain axis in HD occurrence and development.

Contribution of CNS and extra-CNS infections to neurodegeneration: a narrative review

Central nervous system infections have been suggested as a possible cause for neurodegenerative diseases, particularly sporadic cases. They trigger neuroinflammation which is considered integrally involved in neurodegenerative processes. In this review, we will look at data linking a variety of viral, bacterial, fungal, and protozoan infections to Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis and unspecified dementia. This narrative review aims to bring together a broad range of data currently supporting the involvement of central nervous system infections in the development of neurodegenerative diseases. The idea that no single pathogen or pathogen group is responsible for neurodegenerative diseases will be discussed. Instead, we suggest that a wide range of susceptibility factors may make individuals differentially vulnerable to different infectious pathogens and subsequent pathologies.

Butyrate as a potential therapeutic agent for neurodegenerative disorders

Maintaining an optimum microbial community within the gastrointestinal tract is intricately linked to human metabolic, immune and brain health. Disturbance to these microbial populations perturbs the production of vital bioactive compounds synthesised by the gut microbiome, such as short-chain fatty acids (SCFAs). Of the SCFAs, butyrate is known to be a major source of energy for colonocytes and has valuable effects on the maintenance of intestinal epithelium and blood brain barrier integrity, gut motility and transit, anti-inflammatory effects, and autophagy induction. Inducing endogenous butyrate production is likely to be beneficial for gut-brain homeostasis and for optimal neuronal function. For these reasons, butyrate has gained interest as a potential therapy for not only metabolic and immunological disorders, but also conditions related to the brain, including neurodegenerative diseases. While direct and indirect sources of butyrate, including prebiotics, probiotics, butyrate pro-drugs and glucosidase inhibitors, offer a promising therapeutic avenue, their efficacy and dosage in neurodegenerative conditions remain largely unknown. Here, we review current literature on effects of butyrate relevant to neuronal function, the impact of butyrate in a range of neurodegenerative diseases and related treatments that may have potential for the treatment of neurodegenerative diseases.